1. Field of Invention
This invention relates to the field of reconstructing existing bridges and highways, specifically to methods for increasing traffic capacity of existing roadways.
2. Prior Art
There are more and more vehicles that are using existing transportation infrastructure every year. Due to a drastic increase in traffic load and volume, traffic capacity of existing roadways is becoming inadequate. At the same time, especially in urban areas, construction of new transportation facilities is severely restricted by environmental regulations, high costs, and existing land development. Therefore, reconstructing existing bridges and highways in order to increase their traffic capacity very often remains the only choice available.
Prior art methods of reconstructing existing roadways in order to increase their traffic capacity involve either widening existing roadways, or erecting new elevated roadways above existing roadways. In urban areas, erecting new elevated roadways is used most frequently, because widening existing roadways is often constrained by right-of-way restrictions and environmental considerations. Various methods and devices have been proposed for erecting elevated roadways above existing roadways, as described in U.S. Pat. Nos. 2,225,186 to N. C. Sorensen (1940), 3,211,110 to R. M. Pierson (1965), 3,301,146 to S. Krug et al (1967), 3,406,616 to E. McLean (1968), 5,846,020 to K. McKeown (1998), 5,960,502 to Y. Sherman et al (1999), and European Patent 424223 to C. Defontaines (1991).
According to the prior art, elevated roadways are usually erected from various types of frames supporting a structural floor system and a roadway deck, or from reinforced concrete box units. Reinforced concrete systems are very heavy, which virtually precludes their use on existing bridges that are not commonly designed to support a substantial additional weight. In addition, curing of field poured concrete joints during erection of the concrete units requires significant time and leads to interruption of existing traffic. Structural steel systems of the prior art provide very few additional travel lanes; some even result in single lanes, channeling traffic. The latter is not at all acceptable as a permanent roadway due to a possibility of car or truck breakdowns.
Furthermore, erecting a new elevated roadway above an existing one using these prior art methods and devices requires at least a partial closure of the existing roadway for extended periods of time during erection, causing severe disruption of existing traffic. Even if traffic were detoured from the existing roadway undergoing reconstruction, traffic would spill over onto adjacent roadways, creating traffic jams and safety hazards resulting in increased air pollution, costly disruption of local businesses, and interference with local traffic.
Transportation authorities, such as Federal, State, and Municipal Departments of Transportation, public and private transportation agencies, that govern existing bridges and highways, recognize the problem of traffic disruption that occurs during reconstruction of existing roadways. And since traffic volumes on existing roadways vary significantly between peak and off-peak traffic, the transportation authorities issue regulations that specify when and how many of existing travel lanes shall be open to traffic, and when and how many of them may be closed with minimal disruption of existing traffic. Generally, all travel lanes of existing roadways are required to be open during periods of peak traffic, from early morning to late afternoon, but a predetermined number of travel lanes are allowed to be closed during periods of off-peak traffic, mostly during night hours, with minimal disruption of existing traffic.
The aforementioned regulations provide a window of opportunity for development of methods of erecting new elevated roadways above existing roadways with minimal disruption of traffic. Prior art has not yet successfully utilized such methods, and as a result, many existing bridges and highways, especially in urban areas, suffer from insufficient traffic capacity and remain functionally deficient for decades.
In accordance with the present invention a new elevated roadway, which comprises a predetermined number of interconnected ramp units and bridging units, is erected above an existing roadway with minimal disruption of existing traffic. The new elevated roadway increases traffic capacity of the existing roadway by providing elevated travel lanes. This method is easily adapted for use on different types of bridges and highways. It is especially valuable in conjunction with car and truck traffic separation, which provides a reduction in design live load and thus compensates for additional weight of the new elevated roadway.
Insufficient traffic capacity of existing roadways is one of the most frequently encountered problems in the field of reconstructing existing bridges and highways. The primary object of the present invention is to provide a novel, simple and economical solution, which increases traffic capacity of existing roadways with minimal disruption of existing traffic. This object is accomplished by developing methods and utilizing devices that, working synergistically, offer a complete realization of the task.
Accordingly, a highly efficient method of erecting a new elevated roadway above an existing roadway with minimal disruption of traffic is provided. In accordance with the preferred embodiment of this method, the new elevated roadway, comprising a predetermined number of interconnected ramp units and bridging units, is erected in multiple steps, mostly during periods of off-peak traffic, and, after completion of each step, it is opened to existing traffic in time for the next period of peak traffic.
The initial step of erecting the new elevated roadway involves erecting at least two entrance/exit ramp units, at least one of which is made moveable. The ramp units are positioned so that an uppermost end of one ramp unit faces an uppermost end of another ramp unit and, when erection of the ramp units is completed, they embody an initial portion of the new elevated roadway that may be opened to traffic, if specified by a transportation authority.
The next step, which is executed during a period of off-peak traffic as specified by the transportation authority, involves closing the previously erected portion of the elevated roadway to existing traffic and creating a gap in the previously erected portion of the elevated roadway by moving the moveable ramp unit along the existing roadway. A bridging unit is then erected in the gap and the moveable ramp is moved back, if necessary, to adjoin the bridging unit. Consequently, an extended portion of the elevated roadway is erected, and it is opened to existing traffic in time for the next period of peak traffic as specified by the transportation authority.
The step of closing a previously erected portion of the elevated roadway to existing traffic during a period of off-peak traffic as specified by the transportation authority, creating a gap in the previously erected portion of the elevated roadway by moving the moveable ramp unit along the existing roadway, erecting a bridging unit in the gap, and opening an extended portion of the elevated roadway to existing traffic in time for the next period of peak traffic as specified by the transportation authority is repeated many times until erection of the predetermined number of the bridging units is completed.
Thus, by utilizing the novel method of the present invention, the new elevated roadway is erected with minimal disruption of existing traffic, because, at each step, the previously erected portion of the elevated roadway is open to existing traffic during periods of peak traffic, and it is closed to existing traffic during periods of off-peak traffic.
Another major object of this invention is to shorten duration of erecting new elevated roadways. This object is achieved by utilizing space underneath previously erected ramp units and bridging units to store construction and safety equipment and materials, and to house construction field offices and staging areas, thereby saving time usually required to move these items and personnel to and from work areas.
This object is also achieved by utilizing the space underneath a moveable ramp unit for performing erecting work during periods of peak traffic. This work may include, for example, preparing an existing roadway for coming erection of bridging units or surveying condition of existing load-carrying structural members of the existing roadway. This work is time-consuming and complex, especially when performed at night, however, when the space underneath the moveable ramp unit is utilized, the work is conducted during day-time, while existing peak traffic flows overhead. As a result the quality of workmanship is improved and erecting work is continuously conducted during periods of peak traffic and periods of off-peak traffic, thereby shortening overall duration of construction.
Still another object of this invention is to make it versatile enough to be used on different types of existing bridges and highways. This object is achieved by minimizing additional dead load applied to these existing structures by utilizing various light-weight structural forms of bridging units and ramp units that amplify the advantages of the novel method of erecting new elevated roadways with minimal disruption of existing traffic.
Bridging units and ramp units are composed of individual structural members such as deck panels, stringers, braces, and of main frames consisting of columns and floor-beams. The main frames, usually of T, double-T (TT), or portal types, are generally oriented transversely to the direction of traffic, and they serve to support other structural members. The main frames and other structural members may be made of steel, aluminum, other light-weight alloys, or fiber reinforced composite materials in order to minimize their weight, which is especially important when elevated roadways are erected over existing bridges.
This object is also achieved by reducing the live load applied to new elevated roadways as well as to existing roadways. This live load reduction is realized by restricting elevated roadway traffic to xe2x80x9cpassenger cars onlyxe2x80x9d traffic and by restricting existing roadway truck traffic to a minimal number of existing travel lanes as specified by the transportation authority. Since a per-lane live load imposed by truck traffic is several times higher than a per-lane live load imposed by xe2x80x9cpassenger cars onlyxe2x80x9d traffic, it is possible to erect a new elevated roadway carrying several additional xe2x80x9cpassenger cars onlyxe2x80x9d travel lanes without overloading the existing structure.
Another object of this invention is to achieve a higher level of safety for workers and motorists during reconstruction of existing roadways, as well as for motorists after the reconstruction is completed. This object is accomplished by adding a sufficient number of new travel lanes, therefore reducing congestion and upgrading Level-Of-Service.
A higher level of safety is also achieved by allowing xe2x80x9cpassenger cars onlyxe2x80x9d traffic on new elevated roadways, thus separating car and truck traffic. Also, natural lines of separation of truck and xe2x80x9cpassenger cars onlyxe2x80x9d traffic are provided on the existing roadways by lines of columns of main frames protected by traffic barriers.
Safety is also improved because construction equipment, materials and personnel need not be moved often to and from work areas, and the workers are protected from traffic by construction traffic barriers.
Furthermore, a separate travel lane designated for xe2x80x9cemergency vehicles onlyxe2x80x9d may be integrated as a safety feature as well.